With the increase in a volume of data system packet traffic whose representative is IP, efficient transmission of data is demanded also of related art communication service providers (carriers) which provide transmission service mainly for voice. Along with the demand, a highly reliable protection method similar to SONET (Synchronous Optical Network) is required also in a data transmission network. Among failure recovery methods in a packet transmission network is an RPR (Resilient Packet Ring) disclosed in Literature 5.
In RPR, an RPR-MAC frame is transferred between nodes in a packet ring (hereinafter simply referred to as a ring). An RPR-MAC frame has a format including a frame as a payload, to which frame, a transmission destination RPR-MAC address, a transmission source RPR-MAC address and the like are added. Frame to be a payload in an RPR-MAC frame is called a user MAC frame. In the following, a user MAC frame will be denoted to as a U-MAC frame. When a node in a ring is to receive a frame from a terminal outside the ring, the node receives a U-MAC frame. Then, the node adds a transmission destination RPR-MAC address, a transmission source RPR-MAC address and the like to the U-MAC frame to generate an RPR-MAC frame and transfers the generated frame within the ring. In the following description, a transmission destination address in a U-MAC frame will be denoted as a transmission destination U-MAC address. Similarly, a transmission source address in a U-MAC frame will be denoted as a transmission source U-MAC address.
In the following, a failure protection method using a related RPR will be described.
FIG. 20 shows an example of an RPR network using a single ring. The ring has an inner ring 101 and an outer ring 102. The inner ring 101 and the outer ring 102 are paths for transferring packets in reverse directions to each other. In addition, the RPR network illustrated in FIG. 20 comprises six RPR nodes 300-1˜300-6 in the ring. To the RPR node 300-1, a terminal 110 is connected and to the RPR node 300-4, a terminal 111 is connected. First, description will be made of operation of transferring a U-MAC frame from the terminal 110 to the terminal 111 when a failure is yet to occur (in a normal state) in the RPR network shown in FIG. 20. RPR-MAC addresses of the RPR nodes 300-1˜300-6 are assumed to be 300-1˜300-6, respectively.
The RPR node 300-1 having received a U-MAC frame transferred from the terminal 110 solves the RPR-MAC address 300-4 of a transmission destination RPR node from a transmission destination U-MAC address of the U-MAC frame. With a learning data base provided in which a correspondence between a U-MAC address and an RPR-MAC address is stored, each node searches an RPR-MAC address corresponding to a transmission destination U-MAC address to solve an RPR-MAC address of a transmission destination RPR node. Subsequently, the RPR node 300-1 adds an RPR-MAC header with a transmission destination RPR-MAC address as 300-4 and a transmission source RPR-MAC address as 300-1 to the U-MAC frame to generate an RPR-MAC frame. Furthermore, the RPR node 300-1 determines to which of an outer ring and an inner ring, the RPR-MAC frame should be transferred to send out the RPR-MAC frame. Assume here that the RPR-MAC frame is to be sent to the outer ring 102.
The RPR node 300-6 having received the RPR-MAC frame refers to a transmission destination RPR-MAC address of the RPR-MAC frame. The RPR node 300-6, since the transmission destination RPR-MAC address (300-4) fails to coincide with the address (300-6) of the node itself, determines that it is not a frame to be dropped by the node itself to transfer the RPR-MAC frame to the subsequent RPR node 300-5. Similarly to the RPR node 300-6, the RPR node 300-5 transfers the RPR-MAC frame to the subsequent RPR node 300-4.
The RPR node 300-4, since the transmission destination RPR-MAC address of the received RPR-MAC frame coincides with the address of the node itself, takes in the RPR-MAC frame and removes an RPR-MAC overhead to transfer the obtained frame as a U-MAC frame to the terminal 111. Thus, the U-MAC frame is transferred from the terminal 110 to the terminal 111.
Next, description will be made of operation executed when a failure occurs in the ring. FIG. 21 is a diagram for use in explaining operation of the ring executed when a failure occurs in the ring. Assume here that the inner ring 101 and the outer ring 102 between the RPR 300-5 and 300-6 develop a fault. A path indicated by a dotted line in FIG. 21 is the same path as a frame transfer path in a normal state shown in FIG. 20.
The RPR nodes 300-5 and 300-6 adjacent to a failure occurrence position sense occurrence of the failure. Then, the RPR nodes 300-5 and 300-6 each transfer a failure notification RPR-MAC frame including its own node RPR-MAC address to the inner ring 101 and the outer ring 102. The RPR nodes 300-5 and 300-6 apply an identifier indicative of being a failure notification RPR-MAC frame as a transmission destination RPR-MAC address of the failure notification RPR-MAC frame. Thus, there occurs a case where to a transmission destination RPR-MAC address of an RPR-MAC frame, an identifier for control is applied. The controlling identifier may be denoted as ┌reserved RPR-MAC address┘ in some cases. Controlling identifier does not indicate an RPR-MAC address of a specific RPR node.
Upon receiving a failure notification RPR-MAC frame from both the inner ring 101 and the outer ring 102, each of the RPR nodes 300-1˜300-6 locates a failure position from topology information and failure detection node information. Then, the node switches a transfer direction of an RPR-MAC frame passing through the failure position. For example, the RPR node 300-1 switches a sending-out ring of an RPR-MAC frame with the RPR node 300-4 as a transmission destination from the outer ring 102 to the inner ring 101. The RPR node 300-1, upon receiving a U-MAC frame from the terminal 110 similarly to the case described in FIG. 20, sends an RPR-MAC frame with a header added to the U-MAC frame to the inner ring 101. The RPR-MAC frame is transferred to the RPR node 300-4 through the RPR nodes 300-2 and 300-3. The RPR node 300-4 removes an RPR-MAC overhead from the received RPR-MAC frame and transfers the obtained frame as a U-MAC frame to the terminal 111. Failure recovery is executed as described in the foregoing to transfer a frame from the terminal 110 to the terminal 111 even at failure occurrence.
Next, a structure of an RPR node will be described. FIG. 22 is a block diagram showing an example of a structure of a related RPR node. The RPR node comprises a packet switch 310, a frame conversion circuit 320, a forwarding engine 330, a ring topology information collection circuit 340, a ring failure information collection circuit 350, an inside ring path determination circuit 360 and an ADM (Add-Drop Multiplexer) 370. The node further comprises a learning data base 321 which stores a correspondence relationship between a U-MAC address and an RPR-MAC address. The node further comprises a forwarding data base 331 which stores a correspondence relationship between a transmission destination RPR-MAC address and an output ring (either one or both of an inner ring and an outer ring).
The packet switch 310, which is a UNI (User Network Interface), executes transmission/reception of a U-MAC frame to/from the terminals through UNI ports 301 and 302. Upon receiving a U-MAC frame through the respective UNI ports 301 and 302, the packet switch 310 concentrates U-MAC frames from the UNI ports 301 and 302 and transfers the frames to the frame conversion circuit 320. In addition, when a U-MAC frame is transferred from the frame conversion unit 320, the packet switch 310 outputs (transmits) the U-MAC frame through an appropriate UNI port (UNI port connected to a terminal as a transmission destination).
When the packet switch 310 receives a U-MAC frame from the terminal and the U-MAC frame is transferred from the packet switch 310, the frame conversion circuit 320 refers to the learning data base 321 to specify a transmission destination RPR-MAC address in the ring based on a transmission destination U-MAC address of the U-MAC frame (i.e. solve the transmission destination RPR-MAC address). Subsequently, the frame conversion circuit 320 adds a header with the RPR-MAC address as a transmission destination RPR-MAC address and its own node address as a transmission source RPR-MAC address (RPR-MAC overhead) to the U-MAC frame to generate an RPR-MAC frame and transfers the RPR-MAC frame to the forwarding engine 330.
In addition, when the ADM 370 receives an RPR-MAC frame within the ring and the RPR-MAC frame is transferred from the ADM 370, the frame conversion circuit 320 removes the RPR-MAC overhead from the RPR-MAC frame to convert the frame into a U-MAC frame. Then, the circuit transfers the U-MAC frame to the packet switch 310.
The forwarding engine 330 determines based on the transmission destination RPR-MAC address of the RPR-MAC frame transferred from the frame conversion circuit 320 whether the RPR-MAC frame is to be sent to the inner ring 101 or the outer ring 102, or to both of the inner ring 101 and the outer ring 102. At this time, the forwarding engine 330 only needs to refer to the forwarding data base 331 to search an output ring (either the inner ring 101 or the outer ring 102 or both) corresponding to the transmission destination RPR-MAC address. Thereafter, the forwarding engine 330 transfers the RPR-MAC frame to the ADM 370 and notifies the ADM 370 of the determined sending-out destination ring.
In the following, information will be referred to as output ring information which indicates that an RPR-MAC frame is to be sent out to the inner ring 101, that an RPR-MAC frame is to be sent out to the outer ring 102, or that an RPR-MAC frame is to be sent out to both the inner ring 101 and the outer ring 102.
The ring topology information collection circuit 340 generates a topology discovery RPR-MAC frame for comprehending an RPR node structure in the ring to transfer the frame to the ADM 370 together with output ring information. When the ADM 370 receives a topology discovery RPR-MAC frame from inside the ring and the topology discovery RPR-MAC frame is transferred from the ADM 370, the ring topology information collection circuit 340 notifies the inside ring path determination circuit 360 of topology information indicated by the topology discovery RPR-MAC frame.
When the ADM 370 receives a failure notification RPR-MAC frame from inside the ring and the failure notification RPR-MAC frame is transferred from the ADM 370, the ring failure information collection circuit 350 notifies the inside ring path determination circuit 360 of failure detection node information indicated by the failure notification RPR-MAC frame. Thereafter, the ring failure information collection circuit 350 outputs the failure notification RPR-MAC frame to the ADM 370 and causes the ADM 370 to send out the failure notification RPR-MAC frame within the ring.
Adjacent RPR nodes transmit/receive failure notification RPR-MAC frames not including failure detection node information to/from each other. When none of failure notification RPR-MAC frames without including failure detection node information is transferred for a fixed time period, the ring failure information collection circuit 350 determines that a failure is detected. Then, the circuit generates a failure information notification RPR-MAC frame with its own node as a failure detection node and outputs the failure information notification RPR-MAC frame and the output ring information to the ADM 370 to cause the ADM 370 to send out the failure information notification RPR-MAC frame within the ring. In addition, in this case, the ring failure information collection circuit 350 transfers information that its own node is a failure detection node to the inside ring path determination unit 360.
Based on topology information notified from the ring topology information collection circuit 340 and failure information notified from the ring failure information collection circuit 350, the inside ring path determination circuit 360 correlates output ring information with a transmission destination RPR-MAC address and registers the correlation in the forwarding data base 331.
The ADM 370 refers to a transmission destination RPR-MAC address of an RPR-MAC frame input from the outer ring 102 to determine whether the RPR-MAC frame should be terminated or not. When determining to terminate the frame, the ADM 370 transfers the RPR-MAC frame to any one of the forwarding engine 330, the ring topology information collection circuit 340 and the failure information collection circuit 350 (to which circuit the transfer should be made depends on a kind of RPR-MAC frame). When determining not to terminate the frame, the ADM 370 sends out the RPR-MAC frame to the same ring as the ring to which the frame is input (the inner ring or the outer ring).
In addition, when an RPR-MAC frame and output ring information are transferred from the forwarding engine 330, the ring topology information collection circuit 340 or the ring failure information collection circuit 350, the ADM 370 sends out the RPR-MAC frame to either the inner ring 101 or the outer ring 102 (or both of them) according to the output ring information.
Such an RPR node realizes such failure recovery as shown in FIG. 21.
Literature reciting techniques related to a ring network include Literature 1 through 4 and the like. Recited in Literature 1 is the technique of making ring soundness known to all the nodes by using a KAB (keep alive bit). Recited in Literature 2 is the technique that when a link between a node inside a ring and a node outside the ring develops a fault, the node inside the ring sends out a frame with a flooding bit set within the ring. Recited in Literature 3 is necessity of notifying a serving node of occurrence of line cut-off. Recited in Literature 4 is deleting an unnecessary transfer table when among a plurality of contact nodes belonging to two rings, an active contact code is switched.
Literature 1: Japanese Patent Laying-Open No. 2003-174458 (paragraphs 0029-0048).
Literature 2: Japanese Patent Laying-Open No. 2004-242194 (paragraphs 0030-0031).
Literature 3: Japanese Patent Laying-Open No. 10-4424 (paragraph 0006).
Literature 4: Japanese Patent Laying-Open No. 2003-258822 (paragraphs 0022-0085).
Literature 5: “IEEE Draft P802.17/D3.3 Part 17: Resilient Packet Ring (RPR) Access Method & Physical Layer Specifications)”, IEEE (Institute of Electrical and Electronics Engineers, Inc), “IEEE Draft P802.17/D3.3”, p. 74, Apr. 21, 2004.
Related RPR techniques enable extremely high-speed failure recovery to be provided for a single ring network. However, the problem is disabling high-speed failure recovery of a failure of an inter-link in a multi-ring with a plurality of rings connected.
FIG. 23 is a diagram for use in explaining an example of a multi-ring network having two rings connected by two inter-links. In the multi-ring network shown in FIG. 23, two rings 401 and 402 are connected through inter-links 403 and 404. The inter-link 403 is used as a living link and the inter-link 404 is a spare inter-link. One ring 401 comprises the RPR nodes 300-1˜300-6, with a terminal 410 connected to the RPR node 300-1. The other ring 402 comprises RPR nodes 300-7˜300-12, with a terminal 411 connected to the RPR node 300-10.
A path (traffic flow) 420 illustrated in FIG. 23 shows a path used in a case of transferring a frame from the terminal 410 to the terminal 411 in a normal state. Type of frame (U-MAC frame or RPR-MAC frame) varies with a position on the path 420. The RPR node 300-1 receives a U-MAC frame from the terminal 410. Then, the RPR node 300-1 adds a header with 300-3 as a transmission destination RPR-MAC address to convert the U-MAC frame into an RPR-MAC frame and transmits the frame directed to the RPR node 300-3. The RPR node 300-3 removes an RPR-MAC overhead of the received RPR-MAC frame to convert the frame into a U-MAC frame. Then, the node sends out the U-MAC frame to the inter-link 403. Upon receiving the U-MAC frame, the RPR node 300-7 adds a header with 300-10 as a transmission destination RPR-MAC address to convert the U-MAC frame into an RPR-MAC frame and sends out the frame to an outer ring 402-outer. The RPR node 300-10 removes the overhead of the arriving RPR-MAC frame to convert the frame into a U-MAC frame and transfers the obtained frame to the terminal 411. As a result, the frame is transferred along the path 420 shown in FIG. 23 in a normal state.
Assume that in this multi-ring network, a failure occurs on the inter-link 403. In a related multi-ring network, the RPR node 300-1 is not allowed to know occurrence of a failure on the inter-link 403 immediately. Therefore, the RPR node 300-1 converts the U-MAC frame from the terminal 410 into an RPR-MAC frame with 300-3 added as a transmission destination RPR-MAC address as in a normal state. As a result, the RPR-MAC frame is terminated at the RPR node 300-3 and not at the RPR node 300-4 at which the frame is to originally arrive. For reaching the RPR node 300-4, a time is required until a correspondence between a U-MAC address of the terminal 411 and an RPR-MAC address is invalidated at a learning data base of the RPR node 300-1 (in general, called an aging time whose time is approximately 5 minutes), so that high-speed failure recovery is impossible. In other words, from when a correspondence relationship between latest U-MAC address and RPR-MAC address is learned until a lapse of the aging time, a correspondence relationship between new U-MAC address and RPR-MAC address can not be learned. Then, after the lapse of the aging time, a broadcast frame is transferred and at that time a correspondence relationship between a transmission source U-MAC address and a transmission source RPR-MAC address is learned. Until the learning is executed, no frame transfer from the RPR node 300-1 to the RPR node 300-4 is allowed to disable high-speed failure recovery.
An exemplary object of the present invention is to provide, in a multi-ring network with a plurality of ring networks connected, a ring network system, a failure recovery method, a failure detection method, a node and a program for a node which enable high-speed failure recovery when a failure occurs between ring networks.